1. Field of the Invention
This invention relates to the field of radio tuners and more specifically to the design of a tuner assembly which is sufficiently rigid to prevent significant frequency deviation caused by flexing and deformation of the support structure.
2. Prior Art
As tuner designs have become more sophisticated and at the same time more standardized, many attempts have been made to eliminate the remaining defects. One of these defects is a tendency for the frequency to shift due to deformation of the supporting structure particularly when selecting predetermined frequencies by operation of the pushbuttons. The criticality of this becomes apparent when it is realized that a longitudinal movement of only 0.0004 inches (0.01 mm) by a core within a coil can cause frequency change of as much as 1 kH. With the necessarily light weight of tuner support structures, a shift of this magnitude can be caused by many factors, pressure against the front support plate being one of the most important. While some previous tuner designs have combined the guide rods for the core carriage assembly with the coil housing, they have still served only for core carriage guidance. Therefore, the ends of the guide rods were merely brought through apertures in the front plate and left free. While this type of design serves for general guidance of the core carriage motion, it does little to stabilize or rigidize the entire structure. In particular, such a design fails to maintain the front-to-back dimension constant or provide improved alignment of the cores within the tuning coils.